The principle is very simple: If you don't use something that costs money to run you "save". Thus if you park your car and take it off the road, you "save" the cost of running a car - but you either stay put or go by other means. If you don't eat you "save" the cost of food, including cooking it - but you go hungry. Similarly, if you prevent your radiators from heating up, you "save" on the cost of running the heating system - but you will have no heat. By implication, the poor who have nothing "save" huge sums. To me, this is a misuse of the word - going without is not a saving, continuing to enjoy something at a reduced cost is.